Joining the navy

Hi ladies, so 18 and I've talked to a recruiter and I'm really considering joining the navy. Thing is, i have to drop a few pounds by mid January. The recruiter said i should drop 30 pounds or lose 3 inches on my waist. Which honestly seems impossible to me but i have to atleast try.

Is there any healthy way i could do this? I know i have to eat clean and exercise. Any advice? I don't want to go down this hole of having poor health because i am trying to lose weight. I want to do this the right way if it's even possible to in such a short amount of time.